Conventional golf balls can be divided into two general classes: solid and wound. Solid golf balls include one-piece, two-piece (i.e., single layer core and single layer cover), and multi-layer (i.e., solid core of one or more layers and/or a cover of one or more layers) golf balls. Wound golf balls typically include a solid, hollow, or fluid-filled center, surrounded by a tensioned elastomeric material, and a cover.
Examples of golf ball materials range from rubber materials, such as balata, styrene butadiene, polybutadiene, or polyisoprene, to thermoplastic or thermoset resins such as ionomers, polyolefins, polyamides, polyesters, polyurethanes, polyureas and/or polyurethane/polyurea hybrids, and blends thereof. Typically, outer layers are formed about the spherical outer surface of an innermost golf ball layer via compression molding, casting, or injection molding.
From the perspective of a golf ball manufacturer, it is desirable to have materials exhibiting a wide range of properties, such as resilience, durability, spin, and “feel,” because this enables the manufacturer to make and sell golf balls suited to differing levels of ability and/or preferences. In this regard, playing characteristics of golf balls, such as spin, feel, CoR and compression can be tailored by varying the properties of the golf ball materials and/or adding additional golf ball layers such as at least one intermediate layer disposed between the cover and the core. Intermediate layers can be of solid construction, and have also been formed of a tensioned elastomeric winding. The difference in play characteristics resulting from these different types of constructions can be quite significant.
Unfortunately, golf ball polymer compositions are often susceptible to irreversible degradation from exposure to oxygen, heat, and/or ultra violet (UV) light. In this regard, UV light can initiate deteriorating photochemical processes in polymers containing UV absorbent groups or impurities. Aromatic isocyanate-based polyurethane and polyurea polymers are particularly vulnerable to discoloration over time from exposure to UV light rays since aromatic structures are inherently unstable and may be found in the reaction product. Meanwhile, UV light can deteriorate surface properties of an ionomeric layer, resulting in durability issues such as poor adhesion between the ionomeric layer and an adjacent layer. And in rubber materials, destructive peroxy radicals can form during the rubber degradation process.
Antidegradants such as UV absorbers, radical scavengers, peroxide decomposers, and quenchers can protect polymers against the harmful effects of degradation. Since each antidegradant class plays a unique role in protecting a golf ball polymer from deterioration, golf ball manufacturers tend to select an antidegradant based on the specific cause of degradation being addressed.
For example, UV absorbers are helpful to absorb or filter damaging light before a chromosphore (the part of a molecule responsible for its color) can be formed. UV absorbers absorb harmful UV light and transform it into harmless heat. Examples include 2-(2-hydroxyphenyl)-benzotriazoles, 2-hydroxy-benzophenones, hydroxyphenyl-s-triazines, and oxalanilides, each of which are characterized by a specific absoprtion and transmission spectrum. A suitable UV absorber should absorb UV light better and faster than the polymer it is added to protect against, and dissipate absorbed energy before undesirable side reactions occur. Meanwhile, peroxide decomposers decompose peroxides into non-radical and stable products, and quenchers accept energy from excited polymer molecules through an energy transfer mechanism and deactivate chromosphores before the excited states can undergo a reaction resulting in degradation.
On the other hand, free radical scavengers can trap radicals before undesirable reactions (polymer degradation) takes place. Suitable free radical scavengers should be capable of trapping radicals and interrupting the chain reaction that can occur in a polymer when an excited chromophore decomposes to form radicals. Free radicals typically (i) react with the polymer and/or atmospheric oxygen, or (ii) remove a hydrogen atom from the polymer thereby initiating a free radical reaction. Examples of conventional free radical scavengers include sterically hindered amines (HALS) and antioxidants. HALS are typically derivatives of 2,2,6,6-tetraamethylpiperidine and react with a free radical to give the stable nitroxyl radical.
Antioxidants can potentially prolong the service life of a broad range of polymers. Common primary antioxidants include amines and phenolic antioxidants, which are chain terminating. Phenolic antioxidants are often used to inhibit thermo-oxidation at higher processing temperatures (e.g., ≥150° C.) and catalyze formation of a stable phenoxy radical to terminate free radical chain reactions initiated in a polymer. Secondary antioxidants, e.g., phosphites, can decompose peroxide.
However, one drawback with conventional antioxidants is that they typically have a non-cyclic mode of action and become inactive after scavenging a single free radical—which inevitably limits service life of the polymer. Additionally, a “phenolic” yellowing or pinking effect can be created in the resulting polymeric material from the amount of suitable phenolic antioxidant necessary to produce a given protective benefit.
Thus, there is a need for golf balls containing versatile ingredients that can cost effectively prolong protection in thermoset polyurethane/polyurea, ionomeric, and/or rubber-based materials against oxygen, heat, and UV light-related degradation and without the common “phenolic” yellowing or pinking effect produced by conventional phenolic antioxidants. The golf balls of the invention address and solve this need.